Traditionally, backlights used as light source devices for apparatuses such as liquid crystal display apparatuses are roughly classified into a direct backlight and an edge light type backlight.
In the direct backlight, a light source is provided directly below a liquid crystal panel. FIG. 18 is a cross-sectional view illustrating a typical direct backlight 301. In the backlight 301, LEDs (light-emitting-diode) 304 serving as a light source are provided on an LED substrate 303 which is provided below a diffuser 302. Light emitted from each of the LEDs 304 is diffused outward by the diffuser 302. Each of the LEDs 304 is not a linear light source such as a cold cathode fluorescent lamp, but a point light source. This allows provision of a so-called regional light control (such as a local dimming control, or an area active control), which controls brightness of backlight regions in sync with brightness of display image areas, respectively, in a liquid crystal display apparatus. As a result, it is possible to significantly improve contrast of a liquid crystal display apparatus and to lower the power consumption. The local dimming control is explained in detail in paragraph [0004] of Japanese Unexamined Patent Application Publication, Tokukai, No. 2007-286627 (date of publication: Nov. 1, 2007). Note that the area active control is another expression of the local dimming control. The area active control and the local dimming control are technically identical to each other. However, it is difficult to make the backlight 301 thinner because a distance T between the LED substrate 303 and the diffuser 302 should be long enough to prevent uneven light emissions of a light source section.
Recently, thicknesses of display apparatuses such as liquid crystal televisions and liquid crystal monitor displays have been reduced. Therefore, a light source for a large-screen display apparatus is in the process of being switched over from a direct backlight to an edge light type backlight.
The edge light type backlight has an arrangement in which (i) a light source is arranged in the vicinity of a frame of a display apparatus, and (ii) the light source emits light into a translucent resin (light guiding plate) which is made of material such as an acrylic resin so as to provide an even light emission within a surface. FIG. 19 is a cross-sectional view illustrating a representative edge light type backlight 401 with use of an LED light source. In the backlight 401, an LED 404 is provided on an LED substrate 403 which is provided on a side of a light guiding plate 402. This allows the light guiding plate 402 to guide upward light emitted from the LED 404. Since the light from the LED 404 is guided upward without increasing a thickness T2 of the light guiding plate 402, a thickness of a liquid crystal display apparatus can be reduced with ease. However, the light guiding plate 402 only allows an entire display screen to emit but allows a regional light control such as the local dimming control to be carried out.
In view of the circumstances, various kinds of backlight arrangements are proposed so as to achieve a thin liquid crystal display apparatus and the regional light control. (refer to Japanese Unexamined Patent Publication, Tokukaihei, 11-288611 (date of publication: Oct. 19, 1999), Japanese Unexamined Patent Publication, Tokukai, 2001-312916 (date of publication: Nov. 9, 2001), Japanese Unexamined Patent Publication, Tokukai, 2001-42327 (date of publication: Feb. 16, 2001), and Japanese Unexamined Patent Publication, Tokukai, 2002-75036 (date of publication: Mar. 15, 2002), for example)
FIG. 20(a) through FIG. 20(d) respectively illustrates tandem type surface light source devices 501, 511, 521, and 531 disclosed in Japanese Unexamined Patent Publication, Tokukaihei, 11-288611. The surface light source device 501 has a plurality of light guiding plates 502; the surface light source device 511 has a plurality of light guiding plates 512; the surface light source device 531 has a plurality of light guiding plates 532; and the surface light source device 521 has an integral light guiding plate 522. Each of the light guiding plates is getting thinner as getting far from a light source. In the surface light source devices 501, 511, 521, and 531, a light source 503 is provided at each step where two adjacent light guiding plates overlap each other. It is possible to carry out light control of each of the light guiding plates 502, 512, 522 and 532, by controlling brightness of each of the light sources. This allows a liquid crystal display apparatus to become thinner and larger.
However, with an arrangement disclosed in Japanese Unexamined Patent Publication, Tokukaihei, 11-288611, a blight line emerges in the vicinity of a light source, as illustrated in FIG. 21. According to Japanese Unexamined Patent Publication, Tokukai, 2001-312916, a light guiding plate is arranged so that a section, on which the light from a light source provided at each step is incident, is extended. This allows the bright line not to emerge.
The FIG. 22(a) through FIG. 22(i) illustrate surface light source devices 601, 611, 621, 631, 641, 651, 661, 671, and 681 each of which is disclosed in Japanese Unexamined Patent Publication, Tokukai, 2001-312916. The surface light source device 601 has a plurality of light guiding plates 602; the surface light source device 611 has a plurality of light guiding plates 612; the surface light source device 621 has a plurality of light guiding plates 622; the surface light source device 631 has a plurality of light guiding plates 632; the surface light source device 641 has a plurality of light guiding plates 642; the surface light source device 651 has a plurality of light guiding plates 652; the surface light source device 661 has a plurality of light guiding plates 662; the surface light source device 671 has a plurality of light guiding plates 672; and the surface light source device 681 has a plurality of light guiding plates 682. Each of the light guiding plates is getting thinner as getting far from a light source 603, and the light source 603 is provided at each step of the light guiding plate(s). For example, as illustrated in FIG. 22(a), the light guiding plate 602 has an extended section 602a which follows a light source 603 provided at a step of the light guiding plate 602. Similarly, each of the light guiding plates 612, 622, 632, 642, 652, 662, 672, and 682 has an extended section. This allows realization of a thin and large-sized liquid crystal display apparatus which is capable of carrying out a regional light control. Moreover, it is possible to prevent a bright line which occurs in the vicinity of a light source in tandem type surface light source devices illustrated in FIG. 20(a) through FIG. 20(d).
FIG. 23(a) and FIG. 23(b) illustrate a backlight 701 disclosed in Japanese Unexamined Patent Publication, Tokukai, 2001-42327. The backlight 701 has a plurality of light guiding plates 702, and a light source 703 is provided between adjacent two light guiding plates 702. The light guiding plate 702 has, in a longitudinal direction, a protruding edge part 704 on its each side on which the light emitted from the light source is incident. This allows realizing a thin and large-sized liquid crystal display apparatus which is capable of carrying out the regional light control.
Further, in order to improve uniformity of brightness within a surface, Japanese Unexamined Patent Publication, Tokukai, 2002-75036 discloses an arrangement in which a light guiding plate has a sloped surface and optimizes an angle of the sloped surface.
FIG. 24(a) and FIG. 24(b) illustrate an illuminating device 801 disclosed in Japanese Unexamined Patent Publication, Tokukai, 2002-75036. FIG. 24(c) illustrates an illuminating device 811 disclosed in Japanese Unexamined Patent Publication, Tokukai, 2002-75036. The illuminating device 801 includes a plurality of light guiding plates 802, and light sources 803 between respective adjacent two light guiding plates 802. This allows the regional light control to be carried out, as illustrated in FIG. 24(b). Further, the light guiding plate 802 has a sloped surface so that brightness within a surface is uniformed by optimizing an angle of the sloped surface. Further, instead of using the light guiding plate 802 of the illuminating device 801, the illuminating device 811 is arranged so that two light guiding plates 812a and 812b are stacked, each of which has a wedge-shaped cross-section. With the arrangement, it is possible to uniform brightness within a surface by optimizing a cross-sectional shape of each of the light guiding plates 812a and 812b. 
Further, Japanese Unexamined Patent Publication, Tokukai, 2007-115695 (publication date: May 10, 2007) discloses arrangements in which edge-light type backlight modules are joined at each step provided between adjacent two light guiding plates. FIG. 25(a) and FIG. 25(b) are cross sectional views illustrating a backlight 901 and a backlight 911, respectively, both of which are disclosed in Japanese Unexamined Patent Publication, Tokukai, 2007-115695. The backlight 901 includes a plurality of light guiding plates 902 and a plurality of light emitting sections 904 each including a light source 903. The backlight 911 includes a plurality of light guiding plates 912 and a plurality of light emitting sections 914 each including a light source 903. The light guiding plates 902 and 912 are connected to the light emitting sections 904 and 914 so as to create a step arrangements, respectively. This allows provision of a large-sized backlight and allows the regional light control to be carried out by adjusting brightness of each of the light sources 903.
Recently, from an environmental viewpoint, a cold cathode fluorescent lamp, that is currently widely used as a light source for a backlight, has been replaced with an LED. However, the conventional arrangement cause a problem that gives rise to complex arrangement in a case where an LED is used as a light source.
Specifically, in a case where an LED is used as a light source in each of the structures disclosed in Japanese Unexamined Patent Publication, Tokukaihei, 11-288611, Japanese Unexamined Patent Publication, Tokukai, 2001-312916, Japanese Unexamined Patent Publication, Tokukai, 2001-42327, and Japanese Unexamined Patent Publication, Tokukai, 2002-75036, a substrate including LEDs (light source section) should be provided in different places, thereby increasing a cost of parts. Further, the number of connections between the substrates increases, so that the structure becomes complicated. This causes a problem that gives rise to high difficulty of assembly work of a backlight.
Moreover, in a case where a plurality of light guiding plates are provided (for example, FIG. 20(a), FIG. 22(c), and FIG. 23 through FIG. 25), additional arrangements are required to support the light guiding plates, respectively. This causes more complex arrangement.